Tuning arrangement

ABSTRACT

The present invention relates to an improved tuning arrangement to linearise the sensitivity to frequency changes within a certain frequency range in response to tuner displacements relative to a resonator body. The tuning arrangement comprises a tuner and/or resonator having a non-uniform distribution of the effective dielectric permittivity along the axis of tuner displacement. The non-uniform distribution of the effective dielectric permittivity is realised by subdividing the tuner into an arbitrary number of sections, each of which distinguishable at least by their geometrical shape and the value and distribution of the dielectric coefficient ε r .

FIELD OF THE INVENTION

The present invention relates to an improved tuning arrangement forfrequency tuning of dielectric resonators utilising, e.g., aTE_(01δ)-mode or a modified TE_(01δ)-mode.

BACKGROUND OF THE INVENTION

Filter units for combining signals in radio base stations areconventionally built up of various units. FIG. 1 shows an example of acombiner unit 10 that is arranged within a chassis 13 consisting of aresonator 15 and a tuner 14, which is movably arranged within saidresonator 15. The tuner 14 is adjusted to a position relative to aresonator axis, in the figure denoted the z-axis, in order to achieve acertain resonator frequency. This adjustment is often performed by meansof a motor unit 11 and a threaded shaft 12 that is connected to saidmotor unit 11 and inserted into a threaded hollowness of the tuner 14 orother wise connected to it such that the radial movement of the shaft12, which is caused by the motor unit 11, can be transformed into alinear movement of the tuner 14 along said resonator axis. Thisarrangement, however, achieves a non-linear frequency tuning andprovides insufficient precision for frequency adjustments.

A tuning arrangement according to the state of the art may consists of aresonator 15 of a first dielectric material comprising a hollownesswithin which a tuner 14 of cylindrical shape and consisting of a seconddielectric material can be inserted. The tuner 14 is movable arrangedalong an axis 12 of displacement, in this example z-axis, and can bemoved within a range from a first position that corresponds to a maximuminsertion into the hollowness of the resonator 15 to a second positionwhere the tuner has been completely protruded out of said resonator. Forthe sake of simplicity, tuner movements are only considered in directionof the positive z-axis. However, it is apparent that is would belikewise possible to adjust the resonator frequency for tuner movementsin the opposite direction.

FIG. 2 illustrates a sketch of the distribution of the electrical fieldfor a TE_(01δ)-mode in a resonator 31 comprising a hollowness 32 withinwhich a tuner could be inserted. It can be observed that the fieldstrength in the resonator hollowness is relatively weak; hence theperturbation of the field in the hollowness allows a tuning of theresonator frequency in a selected band. The resonator frequency dependson the dielectric properties of the building block consisting ofresonator and tuner, in particular on the choice of the dielectricmaterials and the amount of the tuner mass that is interposed in theresonator hollowness. Frequency adjustments are achieved by varying theamount of dielectric material within the resonator hollowness. The maininfluence results from the resonator while the variation of the tunerposition is applied for precision adjustments of the desired resonatorfrequency. For instance, each tuner position within the resonatorimplies a certain amount of dielectric material in the resonatorhollowness and corresponds thus to a certain resonator frequency. Thesize of the frequency change depends on the amount and the dielectricproperties of the protruded part of the tuner. The resonator frequencyincreases as long as the tuner is protruded out of the resonatorhollowness within the tuning area.

A known system for tuning high-frequency dielectric resonators has beenpresented in EP 0 492 304. Said system comprises a male dielectricresonator having an external diameter d that penetrates to a certaindegree p into a female dielectric resonator having an external diameterD. U.S. Pat. No. 4,728,913 shows another dielectric resonator which iscapable of adjusting the dielectric resonator frequency through a widerfrequency range without deteriorating Q₀.

SUMMARY OF THE INVENTION

In tuning arrangements according to the state of the art, a certaindisplacement of the tuner from a position relative to the resonator doesnot cause the same change of the resonator frequency for each of thepossible tuner positions.

It has thus been observed to be a problem that the precision of anadjustment of the resonator frequency in such tuning arrangements isdifferent for each of the various possible resonator frequencies, i.e.tuner positions.

Therefore, it is the overall object of the present invention to achievea tuning arrangement that can be modified in such a way that theresonator frequency versus tuner position characteristic is adjusted toa desired form for a selected frequency band.

In particular, it is an object of the present invention to achieve atuning arrangement comprising at least one tuner part and at least oneresonator part wherein a displacement of the tuner along its axis ofdisplacement results in almost proportional changes of the resonatorfrequency for a selected range of the possible tuner positionscorresponding to the various resonator frequencies.

Briefly, the present invention bases on the insight that non-linearchanges of the resonator frequency can be equalised or intensified by anon-uniform distribution of the dielectric properties of the tunerand/or resonator along the axis of tuner displacement. This is put intopractice by means of subdividing the tuner and/or the resonator intosections whereby the non-uniform distribution of the dielectricproperties is achieved by means of modifying the shape and/or dielectricpermittivity ε_(r) of the applied material for selected sections of thetuner and/or the resonator.

It is a first advantage of the tuning arrangement according to thepresent invention that the tuning precision for the resonator frequencycan be adjusted to be almost constant for the selected frequency range.

It is another advantage that the tuning arrangement according to thepresent invention implies fewer demands on the mechanical constructionof the parts of the tuning arrangement.

The invention will now be described in more detail by help of preferredembodiments and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an arrangement within which the present invention can beapplied comprising a resonator and a tuner according to the state of theart.

FIG. 2 shows the distribution of the electrical field in a resonator fora TE_(01δ)-mode.

FIG. 3 a shows an example of a general tuner structure and FIG. 3 bshows an example of a general resonator structure according to thepresent invention.

FIGS. 4 a-4 c show three embodiments of tuner object according to thepresent invention.

FIG. 5 a shows a further embodiment of a tuner object according to thepresent invention.

FIGS. 5 b and 5 c show two examples of a distribution of the dielectricpermittivity in a tuner section.

FIGS. 6 a-6 c show three embodiments of tuner objects coming from acombination of features of the first and second embodiment.

FIGS. 7 a and 7 b show still to further embodiments of a resonatorobject according to the present invention.

FIGS. 8 a-8 c show three embodiments of a tuner object according to thepresent invention comprising tuner objects that are arranged outside ofthe resonator.

FIG. 9 shows an example of yet another embodiment of a tuner objectaccording to the present invention.

FIGS. 10 a and 10 b show frequency curves for the relation between tunerposition and resonator frequency of a tuning arrangement according tothe state of the art compared to the curves for two embodiments of thepresent invention.

DETAILED DESCRIPTION

The tuning arrangement according to the present invention intends toachieve an adjustable sensitivity to changes Δz of the tuner positionfrom various starting points z_(i) (i=1, 2, . . . ) with regard to theresulting changes Δf(z_(i)) of the resonator frequency f. As indicatedin FIGS. 10 a and 10 b the sensitivity s and its dependency on the tunerposition z_(i) can be represented by the inclination of the curve of theresonator frequency f with respect to the tuner position z_(i) withinthe tuned bandwidth [f_(min);f_(max)], i.e.$s = {\left. {\frac{\mathbb{d}f}{\mathbb{d}z}(z)} \middle| z \right. = {z_{i}.}}$

The description of the present invention refers mainly to a tuningarrangement for a TE_(01δ)-mode or modifications thereof. However, it isnotwithstanding possible to apply the principles of the presentinvention also for other modes existing in the arrangement.

The preferred embodiments of the present invention can be realised bymeans of several alternatives that intend to achieve an almost lineardependency within a selected frequency range, i.e. an almost constantsensitivity within the tuned bandwidth [f_(min);f_(max)], between achange Δz of the tuner position along an axis of displacement and thecorresponding frequency change Δf. The curve 102 in FIG. 10 aillustrates an example where said linear dependency shall be achievedover the entire tuneable frequency range while the curve 103 in FIG. 10b relates to a case where said sensitivity shall be selectivelyincreased for tuner positions that correspond to a distinct frequencyrange Δf within the tuned bandwidth.

As illustrated by the first frequency curve 101 in FIGS. 10 a and 10 b atuning arrangement according to the state of the art has a lowsensitivity to frequency changes Δf(z_(i)) for resonator frequenciescorresponding to tuner positions, e.g. z₁, that are close to z=z_(min),i.e. a major part of the tuner is still inserted within the resonator.However, this sensitivity becomes comparatively much higher forresonator frequencies that correspond to tuner positions, e.g. z₂, wherethe tuner has been partly removed from said resonator, i.e. for largervalues of z. Therefore, the basic form of the preferred embodimentaccording to the present invention is a tuner or resonator where a tunerdisplacement causes in an initial phase a faster decrease of the totaldielectric properties than in a later phase when, e.g., a part of thetuner already has been protruded from said hollowness. This is achievedby a tuner or resonator comprising a non-uniform distribution of thevolume and/or the dielectric permittivity along the z-axis. Thenon-linearity of the relation between tuner displacement Δz and changeof the resonator frequency Δf(z_(i)), as demonstrated by the frequencycurve 101, can thus be equalised by a non-uniform distribution of thedielectric properties of the tuner and/or resonator along the axis oftuner displacement.

FIG. 3 a shows an example of a general embodiment of a tuner accordingto the present invention. The tuner can be assumed to be realised withinan appropriate three-dimensional body 31, preferably of a form that issymmetric to its longitudinal z-axis 33, e.g. comprising a circular,trapezoidal, oval, quadratic or other cross sections not regular inshape. According to the basic idea of the present invention, thenon-linear frequency changes in response to tuner displacements relativeto a resonator body are equalised by means of a tuner comprising anon-uniform distribution of the dielectric properties along the axis oftuner displacement. Such a tuner object is formed by means ofsubdividing said body 31 into an arbitrary number of sections 311-314,each of which comprising certain dielectric properties, which isachieved by means of varying the volume and/or the dielectricpermittivity εr of said sections. The dielectric properties of such atuner consisting of a number of sections can be described by help of theconcept of an effective dielectric permittivity, which denotes theeffective dielectric permittivity of various tuner portions, e.g. indirection of the tuner displacement, that are composed of one or moresections comprising different dielectric permittivities. An increasedeffective dielectric permittivity of a tuner portion causes thus anincreased sensitivity to frequency changes while a comparatively lowereffective dielectric permittivity of a tuner portion causes a decreaseof the frequency sensitivity in respective tuner positions.

The various tuner sections are limited by means of surfaces that can bedescribed by help of a set of three-dimensional functions f_(s)(x,y,z).Here such functions denote the horizontal surfaces 321 and verticalsurfaces 322 a,322 b. Additionally, each section 311-314 can further bedescribed by means of a function for the distribution of the dielectricpermittivity ε_(r)(x,y,z). A section can, e.g., consist of a materialhaving a homogeneous dielectric permittivity or comprise an increase ordecrease of said permittivity towards a certain direction within thesection. It is especially possible that certain sections 313,314 areair-filled, i.e. ε_(r)≈1. The material used to build a section ischaracterised here for simplicity by its real part ε_(r) of complexrelative permittivity. But in general, material properties arecharacterised by the complex permittivity ε_(c)=ε′−jε″ whereε′=ε_(r)*ε₀, ε″=σ/ω, σ is material conductivity and ω angular frequency.This description allows one to classify a material as almost perfect orgood dielectric when σ/ωε′

1 or as a good conductor when σ/ωε′

1 is valid. However, in certain cases one or several sections can bebuild of materials regarded as almost perfect or good conductors i.e.materials for which only the imaginary part of ε_(c) exist i.e. ε″=σ/ωand these materials are usually characterised by the value of materialconductivity σ at certain frequency.

In some cases the functions describing the section surfaces f_(s)(x,y,z)and the distribution of the dielectric permittivity ε_(r)(x,y,z) in thesections can be easier presented in other coordinate system than therectangular x,y,z coordinate system used in this application, e.gcylindrical coordinate system.

The example shown in FIG. 3 a shows a tuner 31 that is symmetric to acertain z-axis and built up of sections having a cylindrical, conical orring form. The tuner consists of two portions whereof each portion inits turn is subdivided into two sections. The sections are horizontallysubdivided by a planar surface 321 and vertically subdivided by asurface 322 a that comprises a cylindrical surface of length l₁ anddiameter d₁ for the upper tuner portion and a conical surface 322 b oflength l₂ and a variable diameter d(z) for the lower tuner portion. Theupper tuner portion comprises thus an inner tuner section 311 of amaterial having a first dielectric permittivity ε_(r1) and a ring-shapedouter tuner section 313, which in this example concentrically surroundssaid inner tuner section and consists of a material having a dielectricpermittivity ε_(r2), e.g. air. Correspondingly, the lower tuner portioncomprises a conical inner tuner section 312 of a material having adielectric permittivity ε_(r3) and a surrounding outer tuner section 314having a dielectric permittivity ε_(r4), e.g. air.

FIG. 3 b shows a similar approach of a general embodiment of a resonatoraccording to the present invention. Correspondingly to the tuneraccording to FIG. 3 a, the resonator is considered as a building blockconsisting of an appropriate number of sections 341-344 characterised bymeans of their geometry, e.g. diameter, thickness, and length, and bymeans of the distribution of the dielectric permittivity ε_(r)(x,y,z) ofthe material that is applied for said sections. As for the tuner object,the sections are defined by help of sets of three-dimensional functionsf_(s)(x,y,z) that denote the horizontal surfaces 351 and the verticalsurfaces 352 a,352 b of the sections, whereby each section can befurther described by means of a distribution function of the dielectricpermittivity ε_(r)(x,y,z).

As an example, the resonator shown in FIG. 3 b is built up of sections341-344 having a cylindrical or ring form. The sections are horizontallyseparated by a planar surface 351 and vertically separated by a surface352 a having a cylindrical surface of length l₁ and diameter d₁ for theupper resonator portion and a cylindrical surface 352 b of length l₂ anddiameter d₂ for the lower resonator portion. The upper resonator portioncomprises thus an inner section 341 of a material having a firstdielectric permittivity ε_(r1) and an outer resonator section 343 of amaterial having a second dielectric permittivity ε_(r2). When assuming atuning arrangement where the tuner is inserted in a resonator hollownessat least one of the inner resonator sections 341 is air-filled, i.e.ε_(r1)≈1. For embodiments where the tuning is performed by a tuner thatis placed outside of the resonator body said section can be filled outwith an other appropriate dielectric material, i.e. ε_(r1)>1.Correspondingly, the lower resonator portion comprises two sections ofdielectric permittivity ε_(r3) and ε_(r4), whereby the inner resonatorsection can be air-filled, i.e. ε_(r3)≈1, for embodiments that require ahollowness throughout the entire resonator body.

Within the scope of the present invention it is notwithstanding possibleto design the tuner and/or the resonator with an arbitrary number ofsections to achieve any desired shape and distribution of the dielectricpermittivity within the material. However, for a tuner according to thepresent invention in general, the geometrical profile or distribution ofthe dielectric permittivity ε_(r) along the axis of tuner displacementmust be designed in such a way that the tuner portion comprising thelargest effective permittivity is the portion that is first protrudedout of the resonator or the portion which is located further withrespect to the resonator body. Correspondingly, for the resonator thegeometrical profile or the distribution of the dielectric permittivityof a resonator along the axis of tuner displacement must be designed insuch a way that the tuner is first protruded out of the resonatorportion that comprises the largest effective dielectric permittivity.

The two general embodiments shown in FIGS. 3 a and 3 b describe thusmodifications, in regard to the conventional cylindrical structures, ofa tuner or resonator with regard to their geometry or the dielectricproperties of the applied material or a combination of thesemodifications. A change of the geometry implies thus a tuner orresonator comprising sections that are filled with a dielectric materialand sections comprising materials having a lower relative permittivity,e.g. air ε_(r)≈1. A change of the dielectric material results in tuneror resonator arrangement which possess at least two portions withdifferent relative dielectric permittivities. Other embodiments mayapply changes of both the geometry and the dielectric permittivity.Further, it is notwithstanding possible to realise a tuning arrangementthat applies all of the suggested modifications at the same time.

A first embodiment of the tuning arrangement according to the presentinvention relates to a cylindrical tuner 41 that is inserted into ahollowness of a resonator 42 and built up of sections of a material withdielectric coefficient ε_(r1) or air-filled sections, i.e. sectionscomprising ε_(r2)≈1. The various alternatives of said first embodiment,as illustrated, e.g., in FIGS. 4 a-4 c, are distinguishable by means ofthe geometric profiles of the section boundaries. According to the firstembodiment, as shown in FIG. 4 a, the non-uniform distribution of thedielectric permittivity in the resonator hollowness depends on thenon-uniform distribution of the dielectric material of the tuner 41. Theupper tuner portion 411 comprises a higher amount of the tuner materialper unit length, and thus a higher effective dielectric permittivity pervolume unit, than the lower tuner portion, which includes a section 412a consisting of the tuner material and an air-filled section 412 b. Whenthe tuner 41 is protruded from a first position, which corresponds to amaximum insertion of the tuner within the resonator hollowness, out ofsaid hollowness in direction of the positive z-axis the reduction of thetuner material from the resonator hollowness is higher approximately aslong as the upper tuner portion 411 is protruded but will becomparatively lower for positions where only the lower tuner portionincluding the air-filled section 412 b is protruded. Accordingly, thesensitivity to frequency changes is comparatively higher in thebeginning and lower at the end of tuner movement that causes thementioned above equalisation of the sensitivity. For the embodimentshown in FIG. 4 a, it has turned out to be beneficial to select for atypical tuned frequency range between 0.4 GHz and 3 GHz and for typicalresonator used in this band the ratio d₁/d₂ of the diameters of thecylindrical tuner from a range approximately between 1.1 and 1.6 and theratio l₁/l₂ of the lengths of the corresponding tuner sections from arange approximately between 0.2 to 0.4.

According to another alternative of the first embodiment the solidcylindrical section 412 a could be replaced by a ring-formed section 422b, as shown in FIG. 4 b, such that an air-filled section 422 a appearswithin said ring-shaped tuner section 422 b. Both alternatives in FIGS.4 a and 4 b apply a cylindrical boundary surface of a diameter d₂ andlength l₂ for the lower tuner portion. Another alternative is acombination of embodiments shown on FIGS. 4 a and 4 b where the lowerportion is composed of a ring section having two air sections locatedinside and outside of the ring section.

In other cases, as shown in FIG. 4 c, the tuner sections can besubdivided by another appropriate three-dimensional surface, e.g., toachieve a conical like form of the inner section 432 a of the lowertuner portion.

FIG. 5 a shows another embodiment of the present invention to achieve anon-uniform distribution of the dielectric permittivity within theresonator hollowness, which is realised by a tuner 51 with two or moresections 511,512 each of which consisting of materials with a differentdielectric permittivity ε_(r1) and ε_(r2) or characterised by adistribution function ε_(r)(x,y,z) of said permittivity. The tunersections are separated by surface 513 that in general can be describedby a three dimensional function f_(s)(x,y,z). The effective dielectricpermittivity of the upper tuner section 511, which is protruded from theresonator hollowness in direction of the positive z-axis, must be higherthan the effective dielectric permittivity of the lower tuner section512. The non-uniform distribution along the z-axis is thus achieved bythe choice of the dielectric permittivity instead of the geometricdimensioning. The distribution of the dielectric permittivity for eachsection can either be constant or, as illustrated in FIGS. 5 b and 5 c,described by help of a three-dimensional distribution function forε_(r). FIG. 5 b illustrates a possible distribution for a tuner sectionfor a certain radius r_(z) of the xy-plane, i.e. for a constant valuefor z, where the permittivity is higher in the centre part of the tunersection compared to the outer section parts. FIG. 5 c illustrates acorresponding curve for the dielectric permittivity in direction of thez-axis for a certain position r_(z) in the xy-plane, which indicates anincrease of the permittivity value in direction of the tunerdisplacement.

For an embodiment consisting of two sections with constant values forε_(r1) and ε_(r2) and presuming a cylindrical tuner, as shown in FIG. 5a, that shall be applied for a typical tuned frequency range between 0.4GHZ and 3 GHz and for a typical resonator structure used in this bandthe value of the dielectric permittivity ε_(r1) is typically selectedapproximately three times higher than the value of the dielectricpermittivity ε_(r2), i.e. ε_(r1)/ε_(r2)≈3, while the ratio l₁/l₂ of thelengths of the corresponding tuner sections is selected from a rangeapproximately between 0.2 to 0.4.

The embodiments presented in FIGS. 4 a-4 c and FIG. 5 a achieve thenon-uniform distribution of the effective dielectric permittivity byapplying either a non-uniform distribution of the dielectric materialalong z-axis or a non-uniform distribution of the dielectricpermittivity along the z-axis. However, it is straightforward to applyboth non-uniform distributions of the dielectric material and dielectricpermittivity in one tuner. This leads to other possible realisations ofthe tuner according to the present invention as shown, e.g., in FIGS. 6a-6 c, which combine the characteristics of the embodiments shown inFIGS. 4 a-4 c and FIG. 5 a.

In certain cases, the tuner embodiments described above can possess apreferably cylindrical hollowness along the z-axis, preferably in thecentre of the tuner. Small modifications of the tuner dimensions arethen required to compensate the lack of material in the hollowness butthe main features of the tuner embodiments are still valid.

Two other conceivable embodiments realise the basic idea of the presentinvention by corresponding modifications of the resonator body 72, asshown in FIGS. 7 a and 7 b. Here, the tuner 71 constitutes, e.g., acylindrical body or a tuner as described above that is inserted withinthe resonator 72. When said tuner 71 is completely inserted within theresonator hollowness and protruded out of said hollowness from thisposition, the sensitivity to frequency changes is comparatively higheras long as the tuner 71 is positioned between the first resonatorsection 722 a,722 b comprising the higher resonator volume per unitlength along the axis of tuner displacement and/or consisting of amaterial of a higher dielectric coefficient ε_(r2) while saidsensitivity is comparatively lower when the tuner 71 is furtherprotruded out of the resonator hollowness and positioned in the secondresonator section 721 a,721 b consisting of a material of a dielectriccoefficient ε_(r1). As indicated above the non-uniform distributionalong the z-axis can be achieved either by means of varying thegeometrical dimensions of the resonator hollowness or by means ofapplying dielectric materials comprising different dielectriccoefficients ε_(r). The embodiment as shown in FIG. 7 a refers to aresonator hollowness comprising a first section 722 a of a narrowerdiameter d₂ in order to increase the amount of dielectric material perunit length and a second section 721 a with a resonator hollowness of alarger diameter d₁ such that there is an additional section of differentdielectric permittivity, in the figure realised by an air-filled space73. A change of the effective dielectric permittivity of a resonatorportion can also be achieved by means of adding or removing resonatormaterial at the resonator outside or at both the resonator inside andoutside.

Regarding the embodiment shown in FIG. 7 a and presuming a typical tunedfrequency range between 0.4 GHZ and 3 GHz and the typical resonator formused in that band the ratio d₁/d₂ for the diameters of the resonatorhollowness for each section can be selected from a range between 1.1 and2.0 and the ratio l₁/l₂ for the corresponding lengths of said sectionscan be selected from a range between 1.5 and 4.5. Correspondingly, thealternative as shown in FIG. 7 b refers to a resonator comprising afirst section 722 b of a dielectric material having a value for thedielectric coefficient ε_(r1) that is higher than the value for thedielectric coefficient ε_(r2) of a second section 721 b consisting of asecond dielectric material. For this embodiment and presuming a tunedfrequency range between 0.4 GHZ and 3 GHz and the typical resonator formused in that band the ratio ε_(r1)/ε_(r2)≈2 and the ratio l₁/l₂ for thecorresponding lengths of said sections can be selected from a rangebetween 1.5 and 4.5.

Still three other embodiments of the present invention relate to atuning element 81 that is placed outside the of the resonator hollownessas shown in FIG. 8 a and FIG. 8 b or partly inserted as shown in FIG. 8c. As explained above, the tuner is applied for a fine-tuning of theresonator frequency by means of affecting the electrical field withinthe resonator. In the embodiments shown in FIGS. 8 a and 8 b the tuner81 affects instead the electrical field outside of the resonator.Although the frequency curve in these cases has a slightly differentshape when compared to curve 101 in FIG. 10 a the main idea of theinvention is valid and can be described as follows. As already mentionedabove, changes of the tuner position result in different changes of theresonator frequency depending on the starting position of the tuner. Inorder to make this dependency more linear, the tuner 81 is built up oftwo or more sections that can be distinguished at least by means oftheir geometrical dimensions and/or dielectric coefficient. The examplein FIG. 8 a shows a tuner 81 comprising a first section 811 a of lengthl₁ and diameter d₁ and comprising a second section 812 a of length l₂and a diameter d₂, which is smaller than the diameter d₁.Correspondingly, the example in FIG. 8 b shows a tuner 81 comprising asection 811 b of a certain length l₁ that consist of a material having afirst dielectric coefficient ε_(r1) that is higher than the dielectriccoefficient ε_(r2) of the material of the second tuner section 812 b oflength l₂. The sections 812 a, 812 b comprising the smaller tuner volumeper unit length along the axis of tuner displacement or a lowerdielectric coefficient cause comparatively smaller changes of theresonator frequency compared to a tuning arrangement with a uniformdistribution of mass and/or dielectric coefficient. The sensitivity tofrequency changes is thus decreased for those tuner positions where suchtuner sections 812 a, 812 b are effective which leads to a linearisationof the frequency curve.

A variant of the tuner embodiments, which is combination of theembodiments presented in FIGS. 8 a and 4 a is shown in FIG. 8 c. In thatcase the tuner affects the fields inside the resonator hollowness andoutside the resonator. The tuner is built up of two or more sectionsthat are distinguished by their geometrical dimensions and/or dielectricpermittivity. The section 812 c, which is built up of a material havinga dielectric coefficient ε_(r1) has a smaller diameter d₂ than thesection 811 c having the larger diameter d₁ and consisting either of asimilar material or a material having a higher dielectric coefficientε_(r2). Section 812 c is inserted in the resonator hollowness at thebeginning of the tuner movement. As for the structures shown in FIGS. 8a and 8 b this tuner causes smaller changes of the resonator frequencyat the beginning of the movement and make thus the frequency curve morelinear.

The invention according to the embodiments and its alternatives asdescribed above focuses on a linear dependency, i.e. a constantsensitivity, between changes of the tuner position Δz and thecorresponding frequency change Δf(z_(i)) for each of the possible tunerpositions z_(i), i.e. within the tuned bandwidth [f_(min);f_(max)].However, for certain cases in might also be conceivable to have analmost linear frequency curve that comprises a larger slope for tunerfrequencies only within a certain range [z₃;z₃+Δz] of tuner positionswithin the resonator, e.g. in order to provide an increased sensitivityto frequency changes for that specific range. An example of such a curve103 is shown in FIG. 10 b. This is achieved by means of a tuner and/orresonator that comprises one or more sections 911 that are distincteither by means of their geometrical dimensions or the dielectriccoefficient ε_(r) of the applied material and arranged at thosepositions of the tuner and/or resonator that they become effective for adesired frequency sub-range Δf(z₃). If the intended non-uniformity shallbe achieved, e.g., by means of a modification of the tuner 91, which isshown for instance in FIG. 9, the modified tuner section 911 must beplaced approximately such that it is protruded out of the resonatorhollowness 92 for the range of tuner positions [z₃;z₃+Δz] thatcorrespond to the frequency range Δf(z₃) for which the sensitivity shallbe modified. The tuner can be generally composed of a larger number ofsuch distinct sections, whereby the non-uniformity of the dielectricproperties along the z-axis is achieved by means of different tunerproportions or materials comprising different dielectric permittivitiesε_(r). Correspondingly, if the intended non-uniformity shall be achievedby means of a resonator modification, the modified resonator sectionmust be approximately placed such that the tuner is protruded out ofthis section for the range of tuner positions that correspond to thefrequency range for which the sensitivity shall be modified.

The frequency curve 102, as shown in FIG. 10 a, is achieved from thecurve 101 for a tuning arrangement according to the state of the art bymeans of increasing the sensitivity for frequency changes Δf(z₁) fortuner positions close to z=z_(min) due to the fact that the sectionshaving the largest mass and/or dielectric coefficient, i.e. in generalthe largest effective dielectric permittivity per unit length, areeffective, i.e. protruded from the resonator hollowness, for said tunerpositions. The sensitivity of the curve 102 decreases, when compared tocurve 101, for positions where the tuner is protruded out of theresonator i.e. for tuner positions close to z=z_(max).

For the frequency curve 103, as shown in FIG. 10 b, the sensitivity to achange Δz of the tuner position is increased for a specific range[z₃;z₃+Δz] of tuner positions, which leads to a corresponding changeΔf(z₃) of the resonator frequency that is higher than it could beachieved by means of a tuning arrangement according to the state of theart as represented by the frequency curve 101.

The invention is not restricted to the embodiments that have beendescribed above and have been shown in the drawings but can be modifiedwithin the scope of the accompanying claims.

1-15. (canceled)
 16. A tuner adapted to equalize non-linear frequencychanges within a desired frequency range in response to tunerdisplacements relative to a resonator body, said tuner comprising: atuner element a non-uniform distribution of the effective dielectricpermittivity along an axis of tuner displacement, said non-uniformdistribution of the effective dielectric permittivity is realised bysubdividing the tuner element into a number of sections, each of whichis distinguishable by their geometrical shape.
 17. The tuner accordingto claim 16, wherein said tuner element is subdivided into sections thatcan be distinguished by the value and distribution of the dielectriccoefficient εr.
 18. The tuner according to claim 16, wherein theeffective tuning area is within a hollowness of the resonator.
 19. Thetuner according to claim 16, wherein the effective tuning area isoutside of the resonator.
 20. The tuner according to claim 18, whereinthe tuner includes two cylindrical sections comprising a ratio d₁/d₂ ofsection diameters within a range from 1.1 to 1.6 and a correspondingratio l₁/l₂ of section lengths within a range from 0.2 to 0.4.
 21. Thetuner according to claim 18, wherein the tuner includes two sectionshaving a constant diameter having a ratio ε_(r1)/ε_(r2) for the valuesof the dielectric coefficients of the sections within a range from 2.5to 3.5 and a corresponding ratio l₁/l₂ for the section lengths within arange from 0.2 to 0.4.
 22. The tuner according to claim 19, wherein thetuner includes two sections comprising a ratio d₁/d₂ for the sectiondiameters within a range from 1.1 to 2 and a corresponding ratio l₁/l₂for the section lengths within a range from 1.2 to 2.8.
 23. The tuneraccording to claim 19, wherein the tuner includes two sections having aconstant diameter comprising a ratio ε_(r1)/ε_(r2) for the values of thedielectric coefficients of the sections within a range from 1.2 to 4 anda corresponding ratio l₁/l₂ for the section lengths within a range from1.2 to 2.8.
 24. The tuner according to claim 16, wherein the tuner isequipped with a hollowness for fastening of an axis.
 25. The tuneraccording to claim 24, wherein the axis of tuner displacement isarranged centrally through the resonator hollowness.
 26. A tuner adaptedto equalize non-linear frequency changes within a desired frequencyrange in response to tuner displacements relative to a resonator body,wherein the resonator comprises a non-uniform distribution of theeffective dielectric permittivity along the axis of tuner displacement.27. The tuner according to claim 26, wherein the non-uniformdistribution of the effective dielectric permittivity is realised bysubdividing the resonator into a number of sections, each of which isdistinguishable at least by their geometrical shape and the value anddistribution of the dielectric coefficient ε_(r).
 28. The tuneraccording to claim 26, wherein the resonator consists of two sectionshaving a constant dielectric coefficient comprising a ratio d₁/d₂ of thediameters of the hollowness in each section within a range from 1.1 to2.0 and a corresponding ratio l₁/l₂ of the section lengths within arange from 1.5 to 4.5.
 29. The tuner according to claim 26, wherein theresonator consists of two sections having a constant diameter, a ratioε_(r1)/ε_(r2) for the values of the dielectric coefficients of thesections within a range from 1.4 to 4 and a corresponding ratio l₁/l₂for the section lengths within a range from 1.5 to 4.5.